Pre-Devensian glacial deposits south of Preseli

Fluvio-glacial sands and gravels (shown in pink) in the area around Llangolman and Maenclochog, to the south of the Preseli upland.

 Some more original field research here, for those who may be interested.......

Thanks to Huw Absalom of Bush Farm, Llangolman for the opportunity to look at his splendid gravels today.  Very interesting indeed.  I have been frustrated for some time because although there are plenty of patches of glacial and fluvio-glacial deposits in the central and southern parts of Pembrokeshire, as shown on the geological maps, they are very seldom exposed for proper examination.  They should be pre-Devensian if we have got our ice limits in the right places -- but hard evidence of great age was required.  

So when I got a message from Sid Howells telling me that Huw wanted somebody to take a look at the gravels in his small pit close to the Church of St Colman, I got onto the phone and organized a visit.  So I have been over there today, and things are starting to look good.

The pit (grid ref SN 115268) is not a commercial one -- it's just used for providing hardcore and concrete ballast for use on the farm.  It's about 30m across and 10m deep, exposing fluvio-glacial gravels and sands in the full height of the face.  It's cut into the top of an undulating terrace which has clearly undergone a long history of erosion, especially on its northern flank, where the slope drops down into a small tributary valley which is part of the Eastern Cleddau river system.  The valley is about 25m deep.  Huw tells me that clay is exposed on the floor of the valley, and that there are also exposures of sand not far from the stream.  It's a reasonable assumption that clay-rich till underlies the sands and gravels.

The exposed gravels are relatively  fine-grained, with no cobble-sized beds or boulder beds -- indicating turbulent but not violent torrential flow.  There are a few interbedded sand horizons, suggesting periods of quieter flow.  The bedding dips quite steeply from NW towards SE -- so this may indicate the presence of an advancing delta front close to an ice edge.  This is supported by the presence of some larger stones in the gravels, up to football size, and quite angular.  There is one large chunk of bluish rhyolite which looks as if it has come from a larger boulder.  I didn't see any striated pebbles, but I would not be surprised if some were to turn up......  But the gravels are packed with erratics, including assorted Fishguard Volcanics, rhyolite, dolerite and one quite distinctive pebble of Carboniferous Limestone.  (Where on earth did THAT come from?)

Typical gravels exposed in the Llangolman quarry face.  Note the overall alignment of long axes from top left to bottom right.  Note also just how many pebbles are heavily weathered if not rotten.

One of the black layers cemented with manganese oxide, above a sand bed about 20 cms thick.  

Fragments of the lowest black "manganese concrete" layers in the quarry, which was so hard that it had to be broken up with a tractor grab.  Note also traces of foxy-red "iron oxide" concrete.

I have never seen so many layers of manganese concrete in a single small quarry face.  There are at least six of them, including one just a metre or so beneath the ground surface.  This fact, together with the extremely rotten character of many of the pebbles in the gravels, is suggestive of great age.  Maybe we are looking at deposits from the Anglian glacial episode of about 450,000 years ago.

Great age is also indicated by the presence of "churned gravels" near the ground surface which have lost all trace of their original bedding, and several distinct fossil ice wedges and frost fissures within which many of the pebbes are "standing" with their long axes vertical.  That is indicative of pebbles falling or sliding down into an open frost track or wedge from which the ground ice has temporarily melted.  The assumption?  Thick and long-lived permafrost -- maybe for many thousands of years.

The two photos above have been annotated to show the outlines of the ice wedge casts.  Each one is between 2m and 3m deep.  Note how the gravels and sands are "churned" within the casts and normally bedded on the flanks.  I have also annotated the surface layer of gravels, where signs of frost heave are abundant.  This layer is sometimes just 50 cms deep, and in other places well over 1m deep.

Next time I visit the pit, Huw has kindly offered to be in attendance with his digger -- so we can go down deeper, and maybe find some till........

And speaking of till, it is exposed on the flank of a small stone quarry at Plascwrt, at SN 118274.  It's clay rich, with smallish pebbles and cobbles some of which are well rounded far-travelled erratics.  It is friable to the touch, and foxy red in colour.  So again the impression is that it is severely weathered as a result of many thousands of years of exposure to weather of many types.....

The reddish till layer above fractured bedrock in the small stone quarry at Plascwrt.  It is clay-rich and contains abundant erratic pebbles.

Tentative conclusion: these are very old glacial deposits which display a quite different combination of features from those exposed on the northern side of Preseli, which are deemed to be of Devensian age.  My guess is that these are of Anglian age -- or maybe Wolstonian.  (That's a glacial episode that we know very little about, at least in Western Britain.)

Rhosyfelin -- the scheduling issue

I think I have got to the bottom of the mystery about the request to Cadw for the designation of Rhosyfelin as a Scheduled Ancient Monument.  I have received a couple of very helpful letters from Cadw, and it seems that something like this has happened. 

Somebody (we don't know who) asked the Director of Cadw and the Head of Historic Environment to visit the dig site and take a look at it -- which they did, presumably during the September dig. 

Subsequently the Cadw archaeological inspectorate was asked to give a considered view on whether the site met the criteria for ancient monument scheduling.  Presumably they must have visited as well.  However, says the letter, "we were unable to do so (ie advise positively) in the absence of archaeological reports or other supporting evidence.  The site therefore remains on our radar for consideration."

The letter also says that no formal request has been received from any external party for scheduling -- and we must accept that statement in good faith.

There are still some interesting questions that might be asked about the timescale and the sequence of events, and I still suspect some "informal involvement" from the National Park.  But I'll now let this matter rest, content in the knowledge that there is no great conspiracy going on, and that Cadw will not do anything precipitate.  What everybody (including Cadw) now wants, it seems, is some written reporting and some hard evidence.......

So thanks are due to Cadw for keeping us in the picture on this.

 

Geology of Britain Viewer -- Craig Rhosyfelin

I'm more and more impressed with the BGS Geology of Britain Viewer:

http://mapapps.bgs.ac.uk/geologyofbritain/home.html

which you can use to zoom in on anywhere in the country so as to pick up on the details of solid or superficial geology or a combination or the two.  The best scale to look at is 1:50,000, since on smaller scales there are some rather strange amalgamations of categories which might leave you confused.  Indeed, some of the classifications are confusing anyway -- but that's not surprising, given the difficulty of classifying either sold rocks of or superficial materials when you are wandering around in the field.

If we look at the screenshot above, we can see the vast spread of till in the lowland between the Preseli ridge and the Brynberian - Crosswell area, confirming my suspicions that the Devensian Irish Sea Glacier did push across this area.  I think the BGS surveyors have got things pretty well right.

And look at the Craig Rhosyfelin area -- we should not be at all surprised to see, exactly at the site of the archaeological dig, a series of different deposits including till, rockfall materials, torrential fluvioglacial materials, and alluvial and colluvial deposits incorporating frost-shattered slope detritus.  Exactly as I have described them.......

By the way, on the map the pink areas are spreads of fluvio-glacial materials.  The light brown areas with relief shading on them show territory where there are no thick sediments but thinnish soils resting directly on bedrock.

Arwel Afanc and the Quarry of Gloom

 Perhaps the "proto-orthostat" at Rhosyfelin was a ping-pong table?  Looks remarkably like it.  But I digress.......

Mindful of the recent learned discussions on this site, I have started work on the latest blockbuster series for the small or large screen.     I am also mindful of the fact that Tony is pitching to be executive producer of the series, or at the very least,  casting director.   That's fine by me -- he clearly has what it takes.

Like all the best blockbuster sagas, the whole thing has to be based on the truth, with a modicum of fantasy added to keep the youngsters happy.  Arwel Afanc is a name that rolls off the tongue nicely, and it has a subtle ethnic ring to it.  There are also resonances with Buffalo Bill, Crocodile Dundee, Tiger Woods, Nigel Molesworth and other heroic figures from the past who are linked with the names of fierce creatures..........

As ever, I am starting from the end and am working towards the beginning.  The conclusion has to be the discovery of a body crushed beneath that gigantic proto-orthostat which was about to be shipped off to Eric the Red in southern Greenland when everything suddenly went wrong.  Whose body was it?  Watch this space......

More about the Afanc

I had omitted to mention, for those who might not know what an Afanc looks like, that a very nasty one appeared in that well-known historical BBC TV documentary series called "Merlin."  This one was created by magic in very dodgy circumstances, and appears to have caused a spot of bother to those great buddies Arthur and Merlin.

Best to leave him undisturbed, if possible, down there in his watery cavern......

Sorry if this upsets those of a sensitive disposition -- but the truth must be told.

The Brynberian Afanc

The fair maid of Brynberian, who allowed herself to be used as bait for the fearsome water monster called the Afanc....

Thinking about myths and legends, as one does from time to time, I recalled that the Afon Brynberian, which flows past Rhosyfelin, rises on the moorland on the northern slopes of Preseli.  There's an ancient tale centred on Bedd yr Afanc and Brynberian Bridge, less than 2 km upstream of Craig Rhosyfelin.  I published this tale in my book of folk tales called THE LAST DRAGON, in 1992.  Here it is again -- make of it what you will.......

(I have told this tale before on this blog, in two different forms, but it seems timely to tell it yet again, since such tales are now being hijacked and converted into official history!)

4.6 The Brynberian Afanc

Not far from Brynberian there is a most unusual burial chamber on the bleak moorland. It is a long, low gallery chamber which is said to have similarities with some of the Neolithic burial chambers of Ireland dating from about 2500 BC. There is no other burial chamber like it anywhere else in Wales. It is shaped like a wedge, and is about 35 feet long. It is called Bedd-yr-Afanc, which may be translated as "Monster's Grave". However, some authorities believe that the word "afanc" originally meant "dwarf", whereas in modern Welsh it means a beaver.

According to a very old legend there was once a terrible water monster which inhabited a deep pool in the stream near Brynberian bridge. It caused great fear in the hearts of local people, stealing sheep and other animals and laying waste the country round about. At last it was decided that the afanc must be slain, and so a plan was set in motion. It was known from ancient history that water monsters could not resist the sight of a fair maiden, so the fairest girl in the village agreed to be used as a bait. At dusk a powerful team of oxen was brought to the vicinity of the pool, while the men of the village set loops of strong iron chains along the river bank, with the chains connected to the oxen.

Later, when the full moon was high in the sky, the locals waited with bated breath for the afanc to appear, as it always did on the night of the full moon. The brave girl sat some way from the river bank, looking very beautiful in the moonlight, and with her long hair falling about her in waves. She felt extremely nervous, for she knew that long ago, according to legend, another afanc in North Wales had torn off the breast of a maiden such as she when it was captured. At last the monster emerged from the pool. Seeing the girl, it was immediately entranced, and lumbered towards her across the dewy grass of the river bank. She waited till the last possible moment, and then with a scream she fled. At the same time a great shout went up from the men who had been hiding nearby, and the oxen strained on the iron chains. The chain loops on the grass closed, and the afanc was caught around its legs. With a roar of fury it tried to return to the sanctuary of its pool, and as it thrashed about it temporarily reached the water. But the oxen were immensely strong, and as they were driven by their master there was no escape for the afanc. Bit by bit the chains were drawn tighter about its body, and bit by bit it was hauled out of the river and up the river bank. Then all the men attacked it, with whatever weapons they could muster -- axes, sickles, spades, scythes, forks and pointed spears.

At last, after a mighty battle, the bloodied monster lay dead on the grass. A rousing cheer echoed around the moonlit countryside, and as the news spread people came from near and far to see the dead beast. Nobody slept much that night; the ale flowed freely, and the celebrations went on until daybreak. Then, in the morning, the oxen hauled the dead monster up onto the moor. In a suitable place the chains were undone, and the creature was buried in a great tomb made of slabs of rock from the mountain. It was covered with stones and earth, and from that day to this the site has been called Bedd yr Afanc.

Date: c 1300? Sources: Rhys p 689, Davies p 325

Glaciation of Rhosyfelin

I was down at Rhosyfelin this morning with geologist John Downes  -- of which more in due course.
But on the matter of glaciation, the signs are more and more obvious.

I got a better photo of the beautiful ice-moulded surface close to the tip of the spur:

I'm not sure how the archaeologists explain away features like this.  Maybe they had apprentice quarrymen in the bad old days, who were given menial tasks like polishing and smoothing rock outcrops, so that they would be really good at it by the time they got to Stonehenge?  The trouble is that there are smoothed and worn surfaces like this all over the place, and many of the bedrock outcrops in the vicinity of the wonderfully-named "proto-orthostat" are equally well worn.  My guess is that the features have been shaped both by glacier ice and by torrential meltwater during deglaciation.

I'm more and more convinced that the abundant rounded and sub-rounded erratics in the till and the fluvio-glacial deposits have come from the west and north-west, where there are many outcrops of dolerite and other volcanic rocks belonging to the Fishguard Volcanic Series.  The upstanding tors of Carnedd Meibion Owen are only about 3 km away,  and there are more dolerites exposed near Pentre Ifan, about 4 km away to the NW.  That would match up with the suggested direction of Devensian ice movement very well.  Next time I go down I hope I'll also have a geologist with me, so that we can look seriously at the likely provenances for the dolerites and also for rocks like this erratic cobble about 6" long:

The lower picture shows a fragment from the same stone, about 2" long.  I think it's an ash or tuff from the Fishguard Volcanics, but I can't be sure until somebody more expert looks at it.  It's  not from Rhosyfelin, I reckon. 

I'm also coming to the view that the grey clay-rich deposit art the base of the sequence on the valley floor MAY be a deposit from a short-lived proglacial lake.  Watch this space.

Another thing I've been pondering on is the orientation of the meltwater channels at Rhosyfelin.  The little one runs NNE, and the big one runs NNE and then swings towards the NW -- and this latter orientation runs directly counter to the direction of Devensian ice flow around 24,000 - 20,000 years ago.  The channels themselves are much older -- I suspect that they date from the Anglian.   The fluvio-glacial materials in the valley are suggestive a powerful meltwater flow -- probably unconstrained by any ice barrier.  So that means the valley carried a large stream at quite a late stage of deglaciation.  This brings up another interesting question -- could the meltwater have come from the melting of a late Preseli ice cap which remained in existence after the dissolution of the Irish sea ice in the area?  That's an intriguing thought.......